1.

Find the ratio in which the line joining thepoints `(1,2,3)a n d(-3,4,-5)`is divided by the `x y-p l a n e`. Also, find the coordinates of the point ofdivision.A. 3:5 internallyB. 5:3 externallyC. 3:5 externallyD. 5:3 internally

Answer» Correct Answer - A
Suppose the line joining the points `P(1,2,3)` and `Q(-3,4,-5)` is divided by the xy-plane at a point `R` in the ratio `lamda:1`. Then the coordinates of `R` are
`((-3lamda+1)/(lamda+1),(4lamda+2)/(lamda+1),(-5lamda+3)/(lamda+1))`…………..i
Since `R` lies on xy plane i.e. `z=0`
`:.(-5 lamda+3)/(lamda+1)=0implieslamda=3/5`
So, the required ratio is `3/5:1` or `3:5` internally.


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